Q: Do children’s vaccines contain mercury (thiomersal)?

A: None of the vaccines on the National Immunisation Program for children under five years of age contain thiomersal.

Thiomersal (or thimerosal) is a preservative that contains a form of mercury. It was used in very small amounts in vaccines from the 1930s onwards, to prevent contamination of vaccines.

Thiomersal has not been used as a preservative in Australian routine childhood vaccinations since 2000.*

Is thiomersal toxic?

A World Health Organization (WHO) expert review found no evidence to suggest that thiomersal in vaccines has caused, or could cause, any serious harmful effects. Nonetheless, thiomersal was removed from childhood vaccines as a precautionary measure.

Concerns had been raised that giving children thiomersal-containing vaccines could expose them to unsafe amounts of mercury.

Mercury can cause toxic effects, but only when it reaches certain levels in the body. Whether this happens depends on the person’s body weight and the amount of mercury that they are exposed to over time. The concern was that if small infants were exposed to thiomersal, they might accumulate unsafe levels of mercury.

After investigating all the data, these concerns were found to be unsupported. Importantly, the form of mercury contained in thiomersal is called ethylmercury. Most reports of safety problems with mercury occurred with a different form called methylmercury, which takes much longer to leave the body.

Thiomersal was removed as a preservative from vaccines to reduce the amount of mercury that babies and children would be exposed to overall (some children may be exposed to mercury in food or the environment).

* Until 2009, the vaccines Infanrix-Hexa and Engerix-B may have contained insignificant trace amounts of thiomersal remaining from the manufacturing process, even though it was not included as a preservative. New thiomersal-free forms of Infanrix-Hexa and Engerix-B were introduced in 2009.

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